If there is a performance hit vs. the older PHP version, it will be an acceptable one.

There are no show-stopping bugs.

Don't believe me? Well the short proof is John's company have their future riding on it. A longer proof is to take a deep look at the code in adodb which is a great way to grasp John's mindset / experience. Otherwise browse the phpeverywhere archives...

It's an interesting standard to set for the adoption of something as beneficial as the move from PHP4 to PHP5, but it is one way to judge the effectiveness. When you see the major applications tailoring their setups for PHP5 environments, it might be time to consider jumping ship yourself...